Documentation: ACPI: move video_extension.txt to firmware-guide/acpi and convert to reST

This converts the plain text documentation to reStructuredText format
and adds it to Sphinx TOC tree.

No essential content change.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 0 insertions, 106 deletions

diff --git a/Documentation/acpi/video_extension.txt b/Documentation/acpi/video_extension.txt
deleted file mode 100644
index 79bf6a4921be..000000000000
--- a/Documentation/acpi/video_extension.txt
+++ /dev/null
@@ -1,106 +0,0 @@
-ACPI video extensions
-~~~~~~~~~~~~~~~~~~~~~
-
-This driver implement the ACPI Extensions For Display Adapters for
-integrated graphics devices on motherboard, as specified in ACPI 2.0
-Specification, Appendix B, allowing to perform some basic control like
-defining the video POST device, retrieving EDID information or to
-setup a video output, etc.  Note that this is an ref. implementation
-only.  It may or may not work for your integrated video device.
-
-The ACPI video driver does 3 things regarding backlight control:
-
-1 Export a sysfs interface for user space to control backlight level
-
-If the ACPI table has a video device, and acpi_backlight=vendor kernel
-command line is not present, the driver will register a backlight device
-and set the required backlight operation structure for it for the sysfs
-interface control. For every registered class device, there will be a
-directory named acpi_videoX under /sys/class/backlight.
-
-The backlight sysfs interface has a standard definition here:
-Documentation/ABI/stable/sysfs-class-backlight.
-
-And what ACPI video driver does is:
-actual_brightness: on read, control method _BQC will be evaluated to
-get the brightness level the firmware thinks it is at;
-bl_power: not implemented, will set the current brightness instead;
-brightness: on write, control method _BCM will run to set the requested
-brightness level;
-max_brightness: Derived from the _BCL package(see below);
-type: firmware
-
-Note that ACPI video backlight driver will always use index for
-brightness, actual_brightness and max_brightness. So if we have
-the following _BCL package:
-
-Method (_BCL, 0, NotSerialized)
-{
-	Return (Package (0x0C)
-	{
-		0x64,
-		0x32,
-		0x0A,
-		0x14,
-		0x1E,
-		0x28,
-		0x32,
-		0x3C,
-		0x46,
-		0x50,
-		0x5A,
-		0x64
-	})
-}
-
-The first two levels are for when laptop are on AC or on battery and are
-not used by Linux currently. The remaining 10 levels are supported levels
-that we can choose from. The applicable index values are from 0 (that
-corresponds to the 0x0A brightness value) to 9 (that corresponds to the
-0x64 brightness value) inclusive. Each of those index values is regarded
-as a "brightness level" indicator. Thus from the user space perspective
-the range of available brightness levels is from 0 to 9 (max_brightness)
-inclusive.
-
-2 Notify user space about hotkey event
-
-There are generally two cases for hotkey event reporting:
-i) For some laptops, when user presses the hotkey, a scancode will be
-   generated and sent to user space through the input device created by
-   the keyboard driver as a key type input event, with proper remap, the
-   following key code will appear to user space:
-
-	EV_KEY, KEY_BRIGHTNESSUP
-	EV_KEY, KEY_BRIGHTNESSDOWN
-	etc.
-
-For this case, ACPI video driver does not need to do anything(actually,
-it doesn't even know this happened).
-
-ii) For some laptops, the press of the hotkey will not generate the
-    scancode, instead, firmware will notify the video device ACPI node
-    about the event. The event value is defined in the ACPI spec. ACPI
-    video driver will generate an key type input event according to the
-    notify value it received and send the event to user space through the
-    input device it created:
-
-	event		keycode
-	0x86		KEY_BRIGHTNESSUP
-	0x87		KEY_BRIGHTNESSDOWN
-	etc.
-
-so this would lead to the same effect as case i) now.
-
-Once user space tool receives this event, it can modify the backlight
-level through the sysfs interface.
-
-3 Change backlight level in the kernel
-
-This works for machines covered by case ii) in Section 2. Once the driver
-received a notification, it will set the backlight level accordingly. This does
-not affect the sending of event to user space, they are always sent to user
-space regardless of whether or not the video module controls the backlight level
-directly. This behaviour can be controlled through the brightness_switch_enabled
-module parameter as documented in admin-guide/kernel-parameters.rst. It is recommended to
-disable this behaviour once a GUI environment starts up and wants to have full
-control of the backlight level.